The surviving Boston bombing suspect was charged as he lay under armed guard
in his hospital bed with using a “weapon of mass destruction” in the attacks
that killed three people and injured more than 200.

Dzhokhar Tsarnaev at his graduation from Cambridge Rindge and Latin High SchoolPhoto: AP

Dzhokhar Tsarnaev could face the death penalty or life imprisonment if convicted on the federal terrorism charges, the Department of Justice said.

The affidavit contained chilling new details about how Tsarnaev calmly waited for the first bomb to explode before walking away from the backpack that allegedly contained the second explosive device - getting out of harm’s way with just seconds to spare.

The White House earlier rejected calls by leading Republicans for Tsarnaev, 19, to be charged as an enemy combatant under the military tribunal system that is used to prosecute foreign terror militants.

Jay Carney, the spokesman for President Barack Obama, said that under US law, an American citizen cannot be tried by military commissions. Tsarnaev, an ethnic Chechen, moved to America with his family in 2002 and became a citizen on Sept 11 last year.

A week after the attacks at the Boston marathon, a federal judge established jurisdiction for a temporary court for Tsarnaev in the hospital room where he is being treated for serious gunshot injuries he sustained before his capture on Friday night. According to the complaint, he suffered injuries to his “head, neck, leg and hand”.

The complaint filed by the Federal Bureau of Investigations charged Tsarnaev with two preliminary counts: use of a weapon of mass destruction - the legal term deployed for the home-made pressure cooker bomb - and malicious destruction of property resulting in death. Further charges are expected to be brought as the investigation proceeds.

In the accompanying affidavit, FBI special agent Daniel Genck laid out how Tsarnaev and brother Tamerlan, 26, who died after a shoot-out with police, were identified from surveillance video and photographs taken near the finish line of the Boston marathon.

The chronology reveals the chilling composure demonstrated by the brothers as they allegedly conducted the final stages of their murderous mission.

At 2.45pm, Dzhokhar Tsarnaev was seen arriving at the site of the second bomb and placing his backpack at his feet. As the crowds watched the race, Tsarnaev glanced at his mobile phone and at one stage apparently took a picture with it.

Approximately 30 seconds before the first blast, he lifted the phone to his ear for a conversation that lasted 18 seconds. Just after the call, those around him all turned their heads in shock and bewilderment towards the location where the first bomb exploded at 2.49pm.

Tsarnaev “virtually alone... appears calm”, the affidavit starts. Only then did he rapidly walk away without his bag. Just 10 seconds later, the second blast ripped through the spectators.

The complaint also detailed how the two men allegedly car-jacked a motorist on Thursday night in suburban Boston, shortly after the FBI released pictures of them as suspects. The older Tsarnaev jumped into the car, pointed a handgun at the driver and said: “Did you hear about the Boston explosion?” and “I did that”.

The two forced the man to withdraw cash from his bank account at an ATM but then he managed to escape when they both got out of the car at a petrol station.

The affidavit states that three more unexploded home-made bombs were recovered from the scene of the later shoot-out with police, including anotherr pressure cooker device containing nails and ball-bearings.